"The atomic bombings of Hiroshima and Nagasaki brought the Second World War to a quick end and therefore saved lives of countless people."
There is no easy way one could either accept or condemn the message delivered by this quotation. The usage of atomic bombs is not a terrible thing in itself at my opinion, not at least if compared with the relatively recent genocides of Rwanda and former Yugoslavia. I think it is actually quite ridiculous to be terrified about things that happened over 50 years ago, considering that even at this very moment people are dying violent deaths in Afganistan, Congo and in many other countries as well.
The main reason why so many people strongly oppose atomic weapons is probably the immense destructive power held by even one atomic warhead. The atomic bomb which was dropped in Hiroshima had "only" the explosive power of about 20 kilotons, which is not much when compared with the modern intercontinental missiles which are able to carry payloads of hundreds of kilotons. Yet even that "inferior" atomic bomb killed over 80.000 human beings at Hiroshima.
One thing that also strongly speaks against the bombings of Hiroshima and Nagasaki is the claim that Japan had already unofficially surrendered before the bombing, and USA just wanted to test the efficiency of their newly developed toy, the atomic bomb.
Still I do not think that those bombings were ultimately a bad thing. Reason for this is that if the mankind had not fully realized the terrifying prowess of this new weapon at that time, there might have been a nuclear war between USA and USSR caused by, for example, the Cuban missile crisis. If that had happened, it would now be too late to regret as the Earth itself would be rendered inhabitable for centuries to come by the nuclear winter.